A piece of music composed with fast and slow granular synthesis.
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It is based on the same principle as sampling. However, the samples are not played back conventionally, but are instead split into small pieces of around 1 to 50 ms. These small pieces are called grains. Multiple grains may be layered on top of each other, and may play at different speeds, phases, volume, and frequency, among other parameters.
At low speeds of playback, the result is a kind of soundscape, often described as a cloud, that is manipulatable in a manner unlike that for natural sound sampling or other synthesis techniques. At high speeds, the result is heard as a note or notes of a novel timbre. By varying the waveform, envelope, duration, spatial position, and density of the grains, many different sounds can be produced.
An example of granular synthesis. Note how the tiny snippets of sound (the grains) are initially distinct, but then blend together, generating a completely new timbre.
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Both have been used for musical purposes: as sound effects, raw material for further processing by other synthesis or digital signal processing effects, or as complete musical works in their own right. Conventional effects that can be achieved include amplitude modulation and time stretching. More experimentally, stereo or multichannel scattering, random reordering, disintegration and morphing are possible.
Dennis Gabor researched how human beings communicate and hear. The result of his investigations was the theory of granular synthesis, although Greek composer Iannis Xenakis claimed that he was actually the first inventor of this synthesis technique. Xenakis was the first to explicate a compositional theory for grains of sound. He began by adopting the following lemma: "All sound, even continuous musical variation, is conceived as an assemblage of a large number of elementary sounds adequately disposed in time. In the attack, body, and decline of a complex sound, thousands of pure sounds appear in a more or less short interval of time." Xenakis created granular sounds using analog tone generators and tape splicing. These appear in the composition Analogique A-B for string orchestra and tape (1959).
Curtis Roads is often credited as the first person to implement a digital granular synthesis engine. Canadian composer Barry Truax was one of the first to implement real-time versions of this synthesis technique.
Graintable synthesis is neither granular nor wavetable synthesis but a combination of the best of both methods. The results are exciting, controllable and texturally extremely varied. The basis of a Graintable is a sampled sound, which has been pre-processed using an extremely academic and complex method. A whole leaflet would be needed just to describe this. Suffice to say, the result is a perfect set of periodic waveforms that, due to the pre-processing, can be manipulated in a variety of ways. The Graintable can be treated as a wavetable: sweep through it, move through it at any speed without affecting pitch, play any little section repeatedly, use it to pick static waveforms, jump between positions etc.
- Csound - comprehensive music software including granular synthesis (overview over granular synthesis opcodes)
- SuperCollider - programming language for real time audio synthesis
- Reaktor - visual programming environment for sampling, granular sampling, sequencing and modular synthesis
- Max/MSP - graphical authoring software for real-time audio and video
- Pure Data (Pd) - graphical programming language for real-time audio and video
- ChucK - audio programming language for real-time audio synthesis
- Real-time Cmix - programming language for real-time audio synthesis, including several algorithms for granular synthesis
- Usine - multi-touch visual programming audio manipulation
- AudioMulch - modular audio software for real-time audio manipulation
- pyo - python module written in C to help digital signal processing script creation 
- "Granular Synthesis" by Eric Kuehnl
- "The development of GiST, a Granular. Synthesis Toolkit Based on an Extension of the FOF Generator" by Gerhard Eckel and Manuel Rocha Iturbide
- Searching for a global synthesis technique through a quantum conception of sound by Manuel Rocha Iturbide
- Going with the Grain a review of 10 granular synthesis programs by Dennis Miller (2008)
- Further articles on Granular Synthesis
- Bencina, R. (2006) “Implementing Real-Time Granular Synthesis,” in Greenbaum & Barzel (eds.), Audio Anecdotes III, ISBN 1-56881-215-9, A.K. Peters, Natick. online pdf
- Roads, Curtis (2001). Microsound. Cambridge: MIT Press. ISBN 0-262-18215-7.
- Miranda, E. R. (2002). Computer Sound Design: Synthesis Techniques and Programming. Oxford: Focal Press. ISBN 0-240-51693-1.
- Roads, Curtis (1996). The Computer Music Tutorial. Cambridge: The MIT Press. ISBN 0-262-18158-4.
- Wilson, Scott (2011). The SuperCollider Book. Cambridge: The MIT Press. ISBN 978-0-262-23269-2.
- "Les techniques granulaires dans la synthèse sonore by Manuel Rocha Iturbide. Doctoral Thesis. University of Paris VIII, Paris France, 1999.
- Digital signal processing
- Micromontage audio montage on the time scale of microsounds
- Texture synthesis, analogous process for images
- Granular Synthesis Resource Web Site
- Iannis Xenakis, Formalized Music: Thought and Mathematics in Composition. Bloomington and London: Indiana University Press, 1971
- Curtis Roads, "The Computer Music Tutorial". Cambridge and London: The MIT Press, 1996
- Barry Truax, “Real-Time Granular Synthesis with a Digital Signal Processor,” Computer Music Journal 12(2) (1988): 14-26. MIT Press.
- pyo python module